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          <h1 class="post-title" itemprop="name headline">Discuz存储型XSS(1)</h1>
        

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        <p>之前提交到某平台的漏洞，现在已经修复</p>
<h1 id="漏洞证明"><a href="#漏洞证明" class="headerlink" title="漏洞证明"></a>漏洞证明</h1><ol>
<li>漏洞需要开启后台四方格功能<br><img src="/blog/img/1.jpeg" alt=""></li>
<li>发表新帖子,在帖子标题中设置为payload<br><code>&amp;#x003c;img src=1 onerror=alert(1)&amp;#x003e;</code></li>
<li>然后在首页鼠标放在帖子准备点击我们刚才的发表的帖子时，触发onmouseover事件，执行我们的代码。<br><img src="/blog/img/2.jpeg" alt=""><h1 id="漏洞分析"><a href="#漏洞分析" class="headerlink" title="漏洞分析"></a>漏洞分析</h1>鼠标放在帖子上准备点击时，触发onmouseover事件。onmouseover事件中调用的showTip函数最终调用到了_showTip函数<br><img src="/blog/img/3.jpeg" alt=""></li>
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<p>_showTip函数中使用getAtrribute取了tip属性值，然后又放入innerHTML。<br>重点是getAtrribute函数获取属性值时会自动解码实体编码后的值，这样<code>&amp;#x003c;img src=1 onerror=alert(1)&amp;#x003e;</code>就变成<code>&lt;img src=1 onerror=alert(1)&gt;</code>。<br><img src="/blog/img/4.png" alt=""></p>
<p>另外此漏洞中的payload只能用<br><code>&amp;#x003c;img src=1 onerror=alert(1)&amp;#x003e;</code><br>而不能用<br><code>&amp;#x3c;img src=1 onerror=alert(1)&amp;#x3e;</code><br>这是由于Discuz中dhtmlspecialchars函数实现问题。<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br></pre></td><td class="code"><pre><span class="line">function dhtmlspecialchars($string, $flags = null) &#123;</span><br><span class="line">	if(is_array($string)) &#123;</span><br><span class="line">		foreach($string as $key =&gt; $val) &#123;</span><br><span class="line">			$string[$key] = dhtmlspecialchars($val, $flags);</span><br><span class="line">		&#125;</span><br><span class="line">	&#125; else &#123;</span><br><span class="line">		if($flags === null) &#123;</span><br><span class="line">			$string = str_replace(array(&apos;&amp;&apos;, &apos;&quot;&apos;, &apos;&lt;&apos;, &apos;&gt;&apos;), array(&apos;&amp;amp;&apos;, &apos;&amp;quot;&apos;, &apos;&amp;lt;&apos;, &apos;&amp;gt;&apos;), $string);</span><br><span class="line">			if(strpos($string, &apos;&amp;amp;#&apos;) !== false) &#123;</span><br><span class="line">				$string = preg_replace(&apos;/&amp;amp;((#(\d&#123;3,5&#125;|x[a-fA-F0-9]&#123;4&#125;));)/&apos;, &apos;&amp;\\1&apos;, $string);</span><br><span class="line">			&#125;  //在这一行又将 &amp;amp; 解码成 &amp;,导致htmlspecailchars和php中的htmlspecailchars函数差异</span><br><span class="line">		&#125; else &#123;</span><br><span class="line">			if(PHP_VERSION &lt; &apos;5.4.0&apos;) &#123;</span><br><span class="line">				$string = htmlspecialchars($string, $flags);</span><br><span class="line">			&#125; else &#123;</span><br><span class="line">				if(strtolower(CHARSET) == &apos;utf-8&apos;) &#123;</span><br><span class="line">					$charset = &apos;UTF-8&apos;;</span><br><span class="line">				&#125; else &#123;</span><br><span class="line">					$charset = &apos;ISO-8859-1&apos;;</span><br><span class="line">				&#125;</span><br><span class="line">				$string = htmlspecialchars($string, $flags, $charset);</span><br><span class="line">			&#125;</span><br><span class="line">		&#125;</span><br><span class="line">	&#125;</span><br><span class="line">	return $string;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure></p>
<p>这个差异可以这么解释<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">htmlspecialchars(htmlspecialchars(&quot;&amp;#x003c;&quot;)); 值是&quot;&amp;amp;amp;#x003c;&quot;</span><br><span class="line">dhtmlspecialchars(dhtmlspecialchars(&quot;&amp;#x003c;&quot;)); 值是&quot;&amp;#x003c;&quot;</span><br></pre></td></tr></table></figure></p>
<p>而上面tip属性值就是两次dhtmlspecialchars了标题的值,输入存到数据库一次，输出时一次。<br><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">tip=dhtmlspecialchars(dhtmlspecialchars(标题));</span><br></pre></td></tr></table></figure></p>
<h1 id="漏洞总结"><a href="#漏洞总结" class="headerlink" title="漏洞总结"></a>漏洞总结</h1><ol>
<li>dhtmlspecialchars函数和实际的htmlspecialchars函数有差异</li>
<li>getAttribute函数会将属性值解码</li>
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